Hybridization in situ is potentially an effective method for the chromosomal localization of genes. The proposed research will test the applicability of hybridization in situ to identify genes of low-multiplicity or unique sequence in the human chromosome complement. The effectiveness of this method is dependent on obtaining purified probes that are sufficiently radioactive to localize homologous chromosome regions. A major part of the research effort is directed towards technical improvements that will allow the stringent requirements for detection to be met. The general feasibility for mapping genes of low-multiplicity has been tested using known sites of globin synthesis in the mouse. The results confirm the genetic location of the mouse globin loci and strongly suggest that the localization of genes of similar multiplicity, as well as sites of viral integration, is possible using hybridization in situ. Corallary studies include a) an investigation of the relationship of rDNA to satellite associations and the disproportionate frequency of aberration and non-disjunction involving the acrocentric chromosomes, and b) gene assignments in other animal systems, particularly non-human primates, as a focus for evolutionary comparison. BIBLIOGRAPHIC REFERENCES: Warburton, D., A.S. Henderson, and K.C., Atwood, 1975. Localization of rDNA and geisma-banded chromosome complement of the white-handed Gibbon, Hylobates lar. Chromosoma 51: 35-40. Atwood, K.C., A.S. Henderson, D. Kacian and E. Eicher, 1975. On the feasibility of mapping low multiplicity genes by in situ hybridization. Cytogenetics and Cell Genetics 14: 279-281.